Excessive cellular excitability underlies a variety of common, often lethal diseases, ranging from epilepsy to cardiac ventricular arrhythmias. Conventional therapeutic efforts to suppress excitability in such disorders center around pharmacological block of selected ion channels, mechanical disruption of an irritable focus, or devices such as pacemakers or defibrillators. Drug block of ion channels, while sometimes effective, is plagued by side effects attributable to the systemic administration of drugs needed only in small areas of the body. Mechanical disruption of epileptic or arrhythmic foci is traumatic, irreversible and often ineffective. Implantable devices designed to terminate hyperexcitation are expensive, and are activated only after the seizure has begun. Thus there is a need in the art for additional means of treating hyperexcitability which are more effective, less invasive, and less expensive.